Cheng Sun

Immune checkpoint blockade has become a promising therapeutic approach to reverse immune cell exhaustion. Coinhibitory CD96 and T‐cell immunoglobulin and ITIM domain (TIGIT), together with costimulatory CD226, bind to common ligand CD155. The balancing between three receptors fine‐tunes immune responses against tumors. In this study, we investigated the expression of CD96, TIGIT, and CD226 in 55 fresh human hepatocellular carcinoma (HCC) samples, 236 paraffin‐embedded HCC samples, and 20 normal human livers. The cumulative percentage, absolute count, and mean fluorescence intensity (MFI) of CD96 + NK cells are significantly increased in the intratumoral tissues of HCC and break the balance between three receptors. Human CD96 + NK cells are functionally exhausted with impaired interferon‐gamma (IFN‐γ) and tumor necrosis factor‐alpha (TNF‐α) production, high gene expression of interleukin (IL)‐10 and transforming growth factor‐beta 1 (TGF‐β1), and low gene expression of T‐bet, IL‐15, perforin, and granzyme B. In addition, blocking CD96‐CD155 interaction specifically increases lysis of HepG2 cells by NK cells. HCC patients with a high level of CD96 or CD155 expression within tumor are strongly associated with deteriorating disease condition and shorter disease‐free survival (DFS) and overall survival times. Patients with a higher cumulative percentage of CD96 + NK cells within tumor also exhibit shorter DFS. High plasma level of TGF‐β1 in HCC patients up‐regulates CD96 expression and dynamically shifts the balance between CD96, TIGIT, and CD226 in NK cells. Blocking TGF‐β1 specifically restores normal CD96 expression and reverses the dysfunction of NK cells. Conclusion: These findings indicate that human intratumoral CD96 + NK cells are functionally exhausted and patients with higher intratumoral CD96 expression exhibit poorer clinical outcomes. Blocking CD96‐CD155 interaction or TGF‐β1 restores NK cell immunity against tumors by reversing NK cell exhaustion, suggesting a possible therapeutic role of CD96 in fighting liver cancer.

: These findings indicate that NKG2A expression is influenced by factors from cancer nests and contributes to NK cell exhaustion, suggesting that NKG2A blockade has the potential to restore immunity against liver tumors by reversing NK cell exhaustion.

The mechanisms linking hepatitis B virus (HBV) and hepatitis C virus (HCV) infection to hepatocellular carcinoma (HCC) remain largely unknown. Natural killer (NK) cells account for 25%-50% of the total number of liver lymphocytes, suggesting that NK cells play an important role in liver immunity. The number of NK cells in the blood and tumor tissues of HCC patients is positively correlated with their survival and prognosis. Furthermore, a group of NK cell-associated genes in HCC tissues is positively associated with the prolonged survival. These facts suggest that NK cells and HCC progression are strongly associated. In this review, we describe the abnormal NK cells and their functional impairment in patients with chronic HBV and HCV infection, which contribute to the progression of HCC. Then, we summarize the association of NK cells with HCC based on the abnormalities in the numbers and phenotypes of blood and liver NK cells in HCC patients. In particular, the exhaustion of NK cells that represents lower cytotoxicity and impaired cytokine production may serve as a predictor for the occurrence of HCC. Finally, we present the current achievements in NK cell immunotherapy conducted in mouse models of liver cancer and in clinical trials, highlighting how chemoimmunotherapy, NK cell transfer, gene therapy, cytokine therapy and mAb therapy improve NK cell function in HCC treatment. It is conceivable that NK cell-based anti-HCC therapeutic strategies alone or in combination with other therapies will be great promise for HCC treatment.

The mechanism underlying persistent hepatitis B virus (HBV) infection remains unclear. We investigated the role of innate immune responses to persistent HBV infection in 154 HBV-infected patients and 95 healthy controls. The expression of NKG2D- and 2B4-activating receptors on NK cells was significantly decreased, and moreover, the expression of DAP10 and SAP, the intracellular adaptor proteins of NKG2D and 2B4 (respectively), were lower, which then impaired NK cell-mediated cytotoxic capacity and interferon-γ production. Higher concentrations of transforming growth factor-beta 1 (TGF-β1) were found in sera from persistently infected HBV patients. TGF-β1 down-regulated the expression of NKG2D and 2B4 on NK cells in our in vitro study, leading to an impairment of their effector functions. Anti-TGF-β1 antibodies could restore the expression of NKG2D and 2B4 on NK cells in vitro. Furthermore, TGF-β1 induced cell-cycle arrest in NK cells by up-regulating the expression of p15 and p21 in NK cells from immunotolerant (IT) patients. We conclude that TGF-β1 may reduce the expression of NKG2D/DAP10 and 2B4/SAP, and those IT patients who are deficient in these double-activating signals have impaired NK cell function, which is correlated with persistent HBV infection.